This invention relates generally to the acquisition of selected power system voltage and current values used by protective relays and similar devices for the protection and/or monitoring of electric power systems, and more particularly concerns the use of multiple voltage and current sources to supply the required voltage and current values.
Conventionally, electric power systems are protected using function-specific protection devices, i.e. protective relays, which are responsive to voltage and current values obtained from the power line. In some cases, a specific protective device is used for only one protective function, while in other cases, a single device is capable of implementing more than one protective function. Each such specific device traditionally has associated hardware elements, including current transformers and voltage transformers (CTs and VTs) to obtain necessary current and voltage input information for the devices. The devices also include the capability of evaluating the performance of the associated CTs and VTs; in the case where one of those elements fails or becomes faulty, the device will disable the particular function/application using the quantities from the failed voltage and/or current determining elements.
Additional local voltage and current elements associated with the relay/device can provide some backup/redundancy, but this is expensive, adds complexity to the overall system and can result in a larger portion of the power system becoming disrupted if these backup elements also fail to operate.
Further, certain protection functions require voltage and current information from other stand-alone protective devices for proper operation. Obtaining these quantities requires custom wiring and programming in the individual devices, which again is expensive and also time-consuming, requiring experienced technical assistance.
Accordingly, the present invention is a system for selecting voltage and current sources for protective relay devices for protection and control of electric power systems, comprising: a local source for obtaining input voltage and input current quantities from a power line suitable as inputs for a local protection application; a receiving member for receiving input voltage and current quantities suitable as inputs for said local protection application from a remote protective relay device source; at least one protective application responsive to selected input voltage and current quantities from the local source or the remote source for performing a protection algorithm thereon and providing output information indicating the result thereof; a transmitter for transmitting output information from the protection application to other protective relay devices; and a selection element for selecting voltage and current input quantities from the local source or the remote source thereof, in accordance with preselected criteria.